Sandwich panels are typically formed from a core sandwiched between two liner sheets. The core may be relatively thick, yet lightweight, as compared to the liner sheets. The liner sheets may be relative thin, yet stiff. Therefore, sandwich panels typically possess relatively high strength and stiffness at relatively low weight. As such, sandwich panels are widely used in various aerospace applications.
Like traditional sandwich panels, acoustic sandwich panels include a core sandwiched between two liner sheets. One of the liner sheets is perforated, while the other liner sheet is not perforated. The core provides bulk and defines a plurality of cavities. The apertures defined by the perforated liner sheet fluidly couple the cavities with the ambient environment. Therefore, when air flows across the perforated liner sheet of an acoustic sandwich panel, the cavities in the core act as Helmholtz resonators and attenuate the sound of the associated airflow. More specifically, core walls between adjacent cavities in the core act as acoustic septa to attenuate the sound of the airflow.
Because of their relatively light weight and sound attenuating capability, acoustic sandwich panels have been used in various industries, including the aerospace industry. For example, acoustic sandwich panels are commonly incorporated into bypass gas turbine aircraft engines, such as into the inlet inner barrels, fan duct walls and/or exhaust nozzles, to attenuate the noise associated with high volume airflows.
From time to time, an acoustic core cell of the core becomes damaged. As an example, a cell wall of an acoustic core cell can crack. A known way to repair the damaged cell wall is to fill the cavity of the acoustic core cell with repair material such as foaming adhesive or potting compound. A drawback with this known way of repairing the damaged cell wall is that the repair material placed into the cavity fouls acoustic septa associated with that cavity. The fouling of acoustic septa has a negative effect on the attenuation capacity of the acoustic sandwich panel. It would be desirable to be able to repair a damaged acoustic core cell of an acoustic sandwich panel without fouling acoustic septa in the cavity of the acoustic core cell.